JPS61240217A - Compact wide angle zoom lens - Google Patents

Abstract

PURPOSE:To make the overall length of a lens small, and also to compensate satisfactorily the performance by satisfying various specified conditions, in a zoom lens which can change a focal distance by moving mechanically the first lens group and the second lens group, and also can keep a focal position constant. CONSTITUTION:A compact wide angle zoom lens is constituted of a variable power system consisting of the first lens group having a negative focal distance and the second lens group having a positive focal distance, and the third fixed lens group which follows said variable power system and magnifies the focal distance of the variable power system in order from an object side. The first lens group consists of a lens group which is placed in positive, the second lens group consists of a lens group which is placed in positive, negative and positive, and a zoom lens which can change the focal distance by moving mechanically the first lens group and the second lens group, and also can keep the focal position constant is obtained. Also, the focal distance f1 of the first lens group, the focal distance f2 of the second lens group, the focal distance fL of the whole system of a long focus side, and a lateral magnification m3 of the third lens group are made to satisfy various conditions shown by expressions (1)-(3).

Description

Detailed Description of the Invention: a. Technical Field The present invention relates to a zoom lens for still cameras, and more specifically, the present invention relates to a zoom lens for still cameras. The present invention relates to a very compact zoom lens with a variable magnification ratio of about 2 times, covering up to a semi-telephoto angle of about 17 degrees.

b. Prior art and its problems As a zoom lens that covers everything from wide-angle to semi-telephoto,
JP-A-59-64811, JP-A-59-142515
The so-called two-group type consisting of a negative first lens group and a positive second lens group, as shown in the Japanese Patent Laid-Open No. 58-9
No. 7016 and JP-A-58-111013, a fixed negative third lens group is further arranged behind the negative first lens group and the positive second lens group (hereinafter referred to as the fixed third group). type).

Many two-group type zoom lenses are known, but Japanese Patent Application Laid-Open No. 59-64811 provides an aspherical surface in the first lens group and reduces the number of elements in the first lens group to 1. This made it possible to reduce the overall length of the lens.

However, since the power of the first lens group is small, the amount of movement of the first lens group during zooming becomes large.
The total length of the lens on the short focal length side cannot be said to be small. In addition, since the amount of focusing movement increases, there is a problem in that the shortest photographing distance cannot be reduced. Since JP-A-59-142515 does not use an aspherical surface, the overall length is longer than JP-A-59-64811. Also, generally speaking, compared to a fixed third group type, a two-group type cannot reduce the amount of movement of the second lens group, which has an aperture, even if the overall lens length can be made the same (more on this later). ).

Group 3 fixed type has recently become known.

However, it is essentially the same as a two-group type zoom lens with a rear converter attached. Japanese Patent Publication No. 58-97016
The 6X4.
Is it because it is a medium-sized camera lens for 5,6X7cIrL?
The total length of the lens is large, and the number of lenses (especially the first lens) is large.
．． There is also a problem that there are many lenses (third lens group). Japanese Unexamined Patent Publication 1983
No.-111013 has the advantage of being compact, but the negative powers of the first and third lens groups are too large, resulting in large fluctuations in spherical aberration and astigmatism when zooming. Furthermore, since the power of the first lens group is too large, the amount of movement of the second lens group is large even though the third lens group is arranged.

In addition, the negative third lens group is not fixed, but moved together with the second lens group toward the object side, as disclosed in Japanese Patent Application Laid-Open No. 5
There are many such systems, such as No. 4-26754 and Japanese Patent Application Laid-Open No. 54-59157, but compared to the fixed third lens group type, there is a problem that the amount of movement of the second lens group having an aperture and the total length of the lens are large.

C1 Purpose The present invention adopts a fixed third group type for the entire system, and is based on the Japanese Patent Laid-Open No. 58-1998-1, which is a fixed third group type with the smallest overall length of the lens.
It has a smaller number of lenses than No. 111013 (the same type as the two-group type JP-A-59-64811 and JP-A-59-142515), the overall length of the lens is smaller, and the performance is better. The purpose is to correct.

Another objective is to reduce not only the overall length of the lens, but also the amount of movement of the second lens group having the diaphragm, thereby making it smaller and lighter, including the lens frame.

Means for Solving the d0 Problem A compact wide-angle zoom lens according to the present invention includes a variable power system comprising, in order from the object side, a first lens group having a negative focal length and a second lens group having a positive focal length; Consists of a fixed third lens group (relay 7 lens system) that follows the variable power system and expands the focal length of the variable power system, the first lens group consists of negative and positive lens groups, and the second lens group The group is positive.
Consists of negative and positive lens groups, the first lens group and the second lens group
In a zoom lens that can change the focal length and keep the focal position constant by mechanically moving the lens group, (3) 1.0 (m3 (1, 13 where fl: focal point of the first lens group) Distance fl: focal length of the second lens group fL: focal length of the entire system on the long focal length side m3: lateral magnification of the third lens group.

In the wide-angle zoom lens having the above characteristics, the first
The lens group consists of three lenses in three groups: two negative meniscus lenses with concave curvature holes on the image side, and a positive meniscus lens with convex curvature holes on the object side, from the object side, and (4) 1.7 ( Nn However, Nn: A lens configured to satisfy the average value of the d-1ine refractive index of the negative lenses in the first lens group, or simply a single negative lens whose image side surface is a concave curvature hole and whose object side surface is a concave curvature hole. It consists of two groups of two positive meniscus lenses each having a convex curvature hole, and is configured to have at least one aspherical surface.

The second lens group includes, from the object side, two positive lenses each having a convex curvature hole on the object side surface, a negative lens having a concave curvature hole on the image side surface, and a positive lens having a convex curvature hole on the image side surface. Group 4
), and (5) 1.65 <Np where Np: d-1 inch of the object side positive lens group in the second lens group
It is configured to satisfy the average value of the refractive index of e.

Furthermore, the third lens group is characterized in that it is composed of only one negative lens.

e0 Functions and Effects of the Invention The present invention is not significantly different from the two-group type Japanese Patent Application Laid-open No. 142515/1983 in terms of the lens configuration of the first lens group and the second lens group, but the power of each lens group is By making it larger, the amount of movement of the first lens group can be reduced, and by placing a fixed third lens group with negative refractive power behind the two-group type, the movement of the second lens group can be reduced. The amount could also be reduced.

The amount of movement of the second lens group (ΔX2) tends to be smaller in proportion than fl when the power of each group is increased, so the amount of movement of the rear group tends to increase. , in the case of a fixed third lens group in which a negative lens is placed in the third lens group, m3〉1. This allows the amount of movement to be reduced.

As is clear from the equation for the amount of movement of the second lens group, the smaller the condition (1), the smaller ΔX2't- can be made, but when the lower limit is exceeded, 1f11 becomes large (fz is the master lens, so Although it is advantageous to reduce ΔX2, ΔX□ (the amount of movement of the first lens group) increases, and the overall length of the lens on the short focal length side and This leads to an increase in the diameter of the front lens, which goes against the trend of compactness. On the other hand, if the upper limit is exceeded, 1f11 is small as in JP-A No. 58-111013,
Even though the third lens group is arranged, ΔXz becomes large and variations in various aberrations during zooming become large.

Condition (2) C relates to the power of the first lens group,
If condition (1) is used alone, condition (1) will be satisfied as long as the power of the first lens group is reduced, so by also constraining the power of the first lens group, the power of the first lens group can be reduced. This is to reduce the amount of movement and the diameter of the front lens. If the lower limit of condition (2) is exceeded, the power of the first lens group becomes too strong and the upper limit of condition (1) cannot be satisfied, and as mentioned above, the power of the first lens group becomes weaker and the upper limit of condition (1) is not satisfied. Fluctuations in various aberrations become large. On the other hand, if the upper limit is exceeded, it is advantageous for correcting and correcting aberrations, but it is against compactness.

Condition (3) is related to the magnification of the third lens group; if the lower limit is exceeded, ΔX2
On the other hand, if it exceeds the upper limit, it is very advantageous to reduce ΔX2, but if only one negative lens is used, the first. This is not preferable because the air generated up to the second lens group is increased by the magnification. If you increase the number of O lenses in the third lens group, for example,
Although it seems possible to exceed the upper limit of condition (3) as in No. 7016, it would increase the cost and go against the purpose of the present invention.

Condition (4) relates to the negative lens group of the first lens group. If the astigmatism in the direction is excessive,
Difficult to correct.

Condition (5) concerns the object-side positive lens group of the second lens group; the more compact it is, the more fluctuations in spherical aberration and coma aberration during zooming will increase when the lower limit is exceeded, which is undesirable. .

f. Examples Examples 1 to 4 of the present invention are shown below. Here, f is the focal length, ω is the half angle of view, r is the radius of curvature of each lens surface, d is the lens thickness or lens spacing, N is the refractive index of each lens, ν is the Abbe number of each lens, and fB is the back Focus.

[Example 1] 1: 3.5-4.5 f=36.0-68. Oω
= 32.3 (17,3゜plane No r
d N ν1 115.
870 1.650 1.83400 37.2
2 26.538 2.202 3 39.330 1.530 1.7725
0 49.64 26.570 2.752 5 26.597 4.463 1.8051
8 25.46 56.948 35.042
~1.507 30.766 3.035 1
．． 71300 53.88 -118.528
2.7009 20.453 2.839 1
．． 72000 43.710 181.433
0.53411 -92.385 4.194
1.80518 25.412 '16.051
5.4913 -55.592 2.044
1.68893 31.114 -23.455
2.28~19.26615 -500.003
1.50 1.51633 64.116
500.003 fB=37.8O Nn = 1.803 Np = 1.
716 [Example 2] 1: 3.5-4.5 f=36.0-68.0
ω=32.3°-17,4° plane No r
d N ν1 115.9
42 1.650 1.83400 37.22
26.340 2.261 3 39.481 1.530 1.7725
0 49.64 26.884 2.671 5 26.676 4.463 1.8051
8 25.46 57.470 35.015
~1.507 30.281 3.053 1
．． 71300 53.88 -119.377
2.7009 20.158 2.824 1
．． 72000 43.710 151.434
0.54011 -99.509 4.058
1.80518 25.412 15.833
5.59113 -55.774 2.041
1.68893 31.114 -23.736
2.272~19.31715 -100.00
0 1.50 1.58913 61.016
-144.907 fB=37.8O Nn = 1.803 Np = 1.71
6 [Example 3] 1: 3.5-4.5 f=36.0-68,
0 ω=32.3°-17.3° Surface No.
r d N ν1
118.281 1.650 1.83
400 37.22 26.270
2.1943 38.570 1.5
30 1.71300 53.84
26.854 2.8285 26.7
21 4.358 1.80518 25
．． 46 54.812 35.016~1
．． 507 30.936 3.025
1.71300 53.88 -119.5
65 2.7009 20.325
2.822 1.72000 43.710
154.724 0.53311
-101.896 4.157 1.80
518 25.412 16.057
5.45813 -56.447 2
．． 006 1.68893'31.114
-24.281 1.55615 7
4.503 1.500 1.51633
64.116 60.914 fB = 38.212 [Example 4] 1: 3.5-4.5 f=36.15-68.
0 ω±32.2°-17.4° Surface No.
r d N ν1
274.724 1.800 1.8340
0 37.22 21.981 3.7903
28.667 5.792 1.8051
8 25.44 80.387 37.795
~1.105 29.105 3.494
1.73400 51.56 -693.812
2.0007 18.841 3.918
1.67003 47.38 72.423
0.7029 -428.538 3.473
1.80518 25.410 15.163
5.55911 153.119 2.558
1.59270 35.312 -36.48
0 1.00~16.81513 -1776.5
73 2.000 1.51633 64.114
236.157 fB = 38.00 Third surface aspherical surface K = -0,34763αz=o,
13675X10-' αz --0,13077X 10-'However, the aspheric function is Nn = 1.834 Np = 1.702

[Brief explanation of drawings]

Figures 1, 3, 5, and 7 are configuration diagrams of lens systems on the short focal length side of Examples 1, 2, 3, and 4 of the present invention, respectively.
4, 6, and 8 are Examples 1 and 2, respectively.
3.4, in which (a) is an aberration diagram on the short focal length side, (b) is an aberration diagram on the intermediate focal length side, and (C) is an aberration diagram on the long focal length side. Patent Applicant: Asahi Kogaku Kogyo Co., Ltd. Figure 1 Figure 2 m Rational Shingeki Station Sine Condition No. 2 Figure 2 Sine Condition Figure 3 Figure 4 Sine Condition Figure 4 Figure 4 Sine Condition No. 5 (!121 Figure 6 Sine condition Figure 6 Figure 6 Positive arc condition Figure 7 Figure 8 Sine condition Figure 8 Figure 8 Positive arc condition Procedure Amendment 6゜December 76, 1985 Otsu.

Claims (1)

[Claims] 1. A variable power system consisting of, in order from the object side, a first lens group having a negative focal length and a second lens group having a positive focal length, and a variable power system following the variable power system. Consists of a fixed third lens group (relay lens system) that expands the focal length of
The first lens group consists of negative and positive lens groups, and the second
The lens group consists of positive, negative, and positive lens groups, and the first
In a zoom lens that can change the focal length and keep the focal position constant by mechanically moving the lens group and the second lens group, (1) 0.5<f_2/|f_1|<0 .63(2)0
．． 75<|f_1|/f_L<1.05(3)1.0<
m_3<1.13 However, f_1: Focal length of the first lens group f_2: Focal length of the second lens group f_L: Focal length of the entire system on the long focal length side m_3: Satisfies the conditions of the lateral magnification of the third lens group A compact wide-angle zoom lens with special features. 2. The first lens group is composed of three lenses in three groups, from the object side, two negative meniscus lenses with a concave image side surface and a large curvature, and a positive meniscus lens with a convex object side surface and a large curvature, and (4)1 .7<@N@_n where @N@_n: d-line of the negative lens in the first lens group
2. A compact wide-angle zoom lens according to claim 1, which satisfies an average value of refractive index. 3. From the object side, the first lens group is composed of two lenses in two groups: one negative lens with a concave image side surface and a large curvature, and a positive meniscus lens with a convex object side surface and a large curvature, and has at least an aspherical surface. A compact wide-angle zoom lens according to claim 1, characterized in that the lens has one surface. 4 The second lens group has 4 lenses in 4 groups from the object side: 2 positive lenses with a convex object side and large curvature, a negative lens with a concave image side and large curvature, and a positive lens with a convex image side and large curvature. and (5) 1.65<@N@_p where @N@_p: d- of the object side positive lens group in the second lens group
4. A compact wide-angle zoom lens according to claim 1, wherein the compact wide-angle zoom lens satisfies the average value of the line refractive index. 5. A compact wide-angle zoom lens according to claims 1 to 4, wherein the third lens group is simply one negative lens.